When using a conventional X-ray computed tomography (to be referred to as CT hereinafter) apparatus, a subject is generally placed on a top plate, as shown in FIG. 8. The X-ray CT apparatus then executes imaging (to be referred to as regular imaging hereinafter). In regular imaging for a subject, the opening portion of the gantry is sometimes provided with a contact sensor to prevent the subject from being caught between the top plate and the gantry. The X-ray CT apparatus has an interlock mechanism which forcibly stops the movement of the top plate or gantry if the subject comes into contact with the opening portion of the gantry.
Recent X-ray CT apparatuses have area detectors. Such an X-ray CT apparatus having an area detector (to be referred to as an ADCT apparatus hereinafter) sometimes images a desired imaging region (e.g., a portion concerning swallowing or a wrist joint portion) while the subject is placed at the back surface side of the gantry (to be referred to as the gantry back hereinafter) and the imaging region is inserted by the operator into a field of view (to be referred to as an FOV hereinafter) in the opening portion of the gantry.
When performing volume imaging of part of the subject placed at the gantry back, the above interlock mechanism does not work, as shown in FIG. 9. More specifically, when imaging a subject placed at the gantry back, the top plate may damage the subject at the gantry back upon movement of the top plate regardless of an operator's intention. The above problem occurs when, for example, the operator erroneously selects an imaging plan concerning helical imaging and the apparatus executes imaging while a subject is placed at the gantry back.